1. Field of the Invention:
The present invention relates to a method for modifying a polyfumaric acid diester, and more particularly to a method for modifying a polyfumaric acid diester by the introduction of carboxyl groups in the polyfumaric acid diester.
2. Related Art Statement:
Known polycarboxylic acids include polyacrylic acid, polymethacrylic acid and polymaleic acid, and they are industrially used as polyfunctional polymers. The known polycarboxylic acids are also cross-linked with metals to form metal salts which are used as viscosity increasing agents, dispersing agents or adhesives. However, these known polycarboxylic acids suffer multifarious problems in syntheses thereof, including difficulties encountered in control of the molecular weights and corrosion problems of the apparatuses used for the syntheses thereof. For instance, in preparation of polyacrylic acid and polymethacrylic acid by the polymerization of acrylic acid and methacrylic acid, the polymerization reaction proceeds too fast with an extremely large exothermic reaction heat to make it hard to control the polymerization reaction. In addition, since both of the monomers and polymers are hygroscopic, the polymers can be prepared only through solution and emulsion polymerization processes, leading to difficulty in purification the resultant polymers.
Although polyacrylic acid or polymethacrylic acid may also be obtained through hydrolysis of polyacrylonitrile, a polyacrylic ester or a polymethacrylic ester, such hydrolysis involves a hydrolyzing step wherein any of the aforementioned materials is hydrolyzed by the use of a strong acid or base, which causes problems in the subsequent purifying step.
On the other hand, polymaleic acid is obtained through polymerization of maleic anhydride. However, since maleic anhydride is scarcely homo-polymerizable when reacted singly, it is usually matrix-polymerized in the presence of a matrix made of, for example polyvinylpyrrolidone. However, even if maleic anhydride is polymerized in the presence of such a matrix, the polymerization degree of the sythesized polymaleic anhydride is low and the synthesized polymaleic anhydride cannot be isolated from the matrix.
On the contrary, polyfumaric acid diesters each having a number average molecular weight of from 1,000 to 200,000 may be easily prepared by any of the bulk, suspension, solution and emulsion polymerization processes. However, since the polyfumaric acid diesters include no intramolecular polar groups, they are poor in reactivity so that it is difficult to improve their properties, such as adhesiveness, heat resistance and rigidity, by reacting them with modifiers.